Killer yeasts secrete toxic proteins. Known as killer toxins, the proteins can eliminate susceptible cells within their own species or related species. The beer-brewing, bread leavening Saccharomyces cerevisiae is also one of the primary killers.
About Yeast
Also known as baker's or brewer's yeast, S. cerevisiae is a single-celled fungus. Considered one of the first domesticated organisms, it's used in production of many fermented foods and drinks such as wine, beer, coffee, bread and chocolate.
In traditional wet processing of coffee, for instance, creators add yeast to facilitate mucilage breakdown before the bean drying process. In chocolate making, the cocoa beans go through a fermentation process in which action of yeasts and bacteria are vital.
In history, the relationship between humans and delectable fermented products goes back to c. 7000 BCE when signs of intentional brewing appear. Yeast use in beer brewing and wine making is recorded in Sumer and other early civilizations by c. 6000 BCE.
The earliest known records of yeast in baking bread comes from ancient Egypt c. 1500 BCE, and China c. 500 BCE. Humans rely on yeasts for inner and outer body workings. This ubiquitous friend who facilitates human life is also a ruthless killer.
Killer Yeast
A killer phenotype in yeast is first discovered in certain strains of Saccharomyces cerevisiae in 1963. Killer yeast toxins can wipe out whole colonies of susceptible cells.
The phenomenon of killer yeast and yeast warfare raises questions about its ecological roles, interactions and possibilities for use. It could be used in medicine and health, for example.
Specifically, killer yeast toxins are polypeptides composed of amino acids. The toxins infiltrate the cell walls of a sensitive cell by making holes in a target cell's membrane, causing the cell to rupture, collapse and die.
Saccharomyces cerevisiae killer cells are immune to their own toxins, enabling them to flourish while competitors perish. The focused attack of killer yeast on sensitive cells is part of the complex dynamics of an unseen microworld ecology.
A strain of killer yeast might effectively kill other, non-killer strains of Saccharomyces cerevisiae, as well as some wild yeast species. The selectivity of these toxins creates an evolutionary advantage, allowing killer strains to dominate.
Killer yeast can reduce competing yeast populations by as much as 80%, giving the killer a critical advantage in its environment. By eliminating other yeast cells, killer yeast gains access to valuable resources like sugars and nutrients.
Resource control functions promote the growth of the killer yeast. For instance, in laboratory settings, Saccharomyces cerevisiae has shown a 40% increase in growth when competing with non-killer strains under nutrient-limited conditions.
Killer Yeast - Favorite Food
Like other yeasts, killer yeast is heterotrophic, meaning it derives its nutrition from organic substrates. Killer yeast feeds mainly on fermentable carbohydrates, particularly glucose.
These sugars are abundant in its natural habitats, which include fruit, soil, and various fermented products. When conditions are favorable, killer yeast metabolizes these nutrients through fermentation.
Killer yeast's ability to outcompete others for sugars ensures its survival and dominance in the environment. The fermentation process produces of over 100 billion liters of beer and wine globally every year.
Killer Yeast in Nature
Killer yeast is found naturally in diverse environments. It forms especially where yeast populations are high, such as in fermented foods, beverages, soil, and plant tissues. The presence of killer yeast and its toxins significantly influences ecological interactions.
In the wild, killer yeast helps regulate the populations of sensitive strains, helping maintain diversity and stability. It often grows on skins of ripe grapes. Yeast doesn't appear on fruit until it's ready to harvest, when the sugars are sweetest.
In grape fermentation, killer yeast can help control spoilage. By ensuring only the strong survive, a higher quality wine is created. Thus the killer attributes of this yeast are overall for the good of humanity.
Killer yeast has a drawback in its potential to turn good booze bad during fermentation. Yeast can be de-activated by lowering fermentation temperatures, using sterile filtration to eliminate yeast from the wine, or fortifying with brandy or neutral spirits to destroy yeast cells.
Killer Hangover
A killer hangover is also indirectly caused by yeast. Acetaldehyde is a compound formed by all yeast. As yeast undergoes fermentation, glucose is turned into pyruvate then acetaldehyde, and finally ethanol.
Ethanol is the alcohol in alcoholic drinks. It's reconverted by the liver into acetaldehyde. If the body can't process the acetaldehyde fast enough, as in a night of heavy drinking, it builds up in the system, causing hangover symptoms such as headache, dizziness and vomiting.
Yeasts With Potential to Kill
Not all yeast species have the ability to produce killer toxins. The capacity to secrete these proteins is restricted to certain strains and species, which have evolved this trait. While many yeasts are more competitive than they look, they're not necessarily lethal.
Relationships among yeasts can vary widely. They range from mutualism, in which the yeasts bond together and form intricate cooperative colonies much like multi-celled organisms, to outright biological warfare.
Killer yeasts share characteristics with other microorganisms. Some other fungi and bacteria also produce toxins to inhibit competitors. In bacterial communities, some strains secrete bacteriocins, or antibacterial proteins, to kill closely related bacteria species.
Certain molds and filamentous fungi are also powerful territorial defenders. They produce mycotoxins to keep others from inhabiting the same space.
Toxic as they are, killer yeasts are not hazardous to humans. As most of the known killer yeasts, particularly Saccharomyces cerevisiae, are widely used in the food industry for baking and brewing, there's no significant evidence these yeasts pose a risk to human health.
However, it can be a cause of vaginitis or pharyngitis. Potentially fatal systemic disease due to S. cerevisiae has been recorded in bone marrow transplant patients and in those immunocompromised as a result of cancer or AIDS.
Facts about Killer Yeast
Discovery: Killer yeast was identified in the 1940s, leading to extensive investigations into its properties and potential applications.
Strains: The most studied killer yeast is Saccharomyces cerevisiae, often used in baking and brewing. Multiple killer strains of S. cerevisiae exist.
Toxins: Killer toxins can vary significantly between different strains, each with distinct toxic effects.
Immune System: Killer yeast has built-in resistance mechanisms that protect it from its own toxins.
Genetic Basis: The genes responsible for toxin production and immunity are often located on plasmids (small DNA molecules within the cell).
Applications: Research into killer yeasts may offer potential applications in biotechnology, such as using killer toxins to manage harmful yeast strains during fermentation.
Killer yeast presents a fascinating case study of microbial competition and adaptation. Through production of potent killer toxins, these yeasts attain of a standard of living higher than that of sheer survival.
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